Membrane unit, housing of a pressure measuring unit and pressure measuring unit

1. A membrane unit configured for use in a housing of a pressure measuring unit for measuring pressure of blood in an extra-corporeal blood circuit, comprising:

a flexible membrane and a fixing ring which is integral with the membrane such that the membrane and the fixing ring form a one-piece element, the fixing ring having a lower flexibility than the membrane and the fixing ring including at least one fixing element for fixing the fixing ring to the housing,

a contact surface between the membrane and the fixing ring being not flat and having at least one projection extending from at least one of the membrane and the fixing ring, the projection engaging with at least one groove in the other of the membrane and the fixing ring.

2. The membrane unit according to claim 1 , wherein the fixing ring and the membrane are secured to each other.

3. The membrane unit according to claim 2 , wherein the fixing ring and the membrane are secured to each other by at least one of gluing and welding.

4. The membrane unit according to claim 1 , wherein the fixing ring and the membrane are configured as a joint manufacture from a common process of manufacture.

5. The membrane unit according to claim 4 , wherein the fixing ring and the membrane are a two-component injection molded manufacture.

6. The membrane unit according to claim 1 , wherein the at least one fixing element of the fixing ring is configured as at least one of a projection, a groove, and a thread.

7. The membrane unit according to claim 6 , wherein the at least one fixing element of the fixing ring is located at an outside area of the fixing ring.

8. The membrane unit according to claim 7 , wherein the fixing ring includes a U-shaped portion, and the fixing element is located on at least one of facing sides of legs of the U-shaped portion.

9. The membrane unit according to claim 1 , wherein the fixing ring is joined perpendicular to the membrane.

10. The membrane unit according to claim 1 , wherein the membrane has a circumferential portion and a central portion, the circumferential portion having a larger thickness than the central portion.

11. The membrane unit according to claim 10 , wherein the sealing lip together with a larger thickness portion in the circumferential portion of the membrane extends into a first direction perpendicular relative to a planar area defined by the central portion of the membrane and the fixing ring extends relative to the planar area in a direction opposite to said first direction.

12. The membrane unit according to claim 1 , wherein the membrane has a circumferentially extending sealing lip for sealing the contact surface between the membrane and said housing.

13. The membrane unit according to claim 12 , wherein the sealing lip of the membrane has a shape that equals a shape of the contact surface between the membrane and the fixing ring.

14. The membrane unit according to claim 1 , wherein the membrane has a groove on the surface facing the fixing ring.

15. A pressure measuring unit comprising a membrane unit according to claim 1 , the fixing elements of the membrane unit engaging with the fixing elements of the housing and the membrane of the membrane unit forming one surface of the pressure measuring chamber of the housing.

16. A housing of a pressure measuring unit for measuring pressure of blood in an extra-corporeal blood circuit, comprising an inlet and an outlet for a fluid the pressure of which is to be measured and a pressure measuring chamber located in fluid communication with the inlet and the outlet, the pressure measuring chamber having an opening that is closable by a membrane inserted into the housing, the housing including fixing elements for fixing the membrane unit according to claim 1 to the housing with the fixing elements being located at at least one of the projections extending around said opening of the pressure measuring chamber.

17. The housing according to claim 16 , wherein the projection extends perpendicularly relative to said opening of the pressure measuring chamber.

18. The housing according to claim 16 , wherein the fixing elements of the projection are configured as at least one of a groove, a jut, and a thread.

19. The housing according to claim 16 , wherein the fixing elements are located on a side of the projection which is oriented to said opening of the pressure measuring chamber.

20. A pressure measuring unit comprising a housing according to claim 16 , the fixing elements of the membrane unit engaging with the fixing elements of the housing and the membrane of the membrane unit forming one surface of the pressure measuring chamber of the housing.